Incomplete cake recipe - what is the missing amount likely to be?

[MenoHiccup]

This is a chocolate cake I learned to make as a child. For years I made it without a recipe. I haven't made it for several years, and now I cannot remember the full recipe!

Can you help me? Nothing was weighed, it was all measured using a glass mug we had. What are the forgotten quantities likely to be?

1 block of butter (English, so likely to have been 8oz)
1 mug of cocoa powder
1? mug of sugar

Melt these all gently together in a saucepan over a low heat.

Meanwhile, separate 6 eggs.

When the mixture is melted, remove from the heat and allow to cool a little while you prepare the cake tin.

Beat the 6 yolks into the mixture. Add a teaspoon of vanilla extract.

Gently mix in ???? glasses of self-raising flour.

In a separate bowl, beat the egg whites until they do not move if you turn the bowl over. Fold the cocoa mixture into the egg whites.

Transfer to cake tin and bake at Gas 4 until it passes the skewer test.

I cannot remember the quantities of sugar and flour.

Thoughts?

I did a bit of maths:

1 block of butter was 8oz
1 cup cocoa is approx 3.5oz
1 cup flour is approx 4.5oz
(Total cocoa+flour=8oz)
1.5 cup sugar is approx 10oz

Which is not far off the 2,2,2 per egg proportions of a standard sponge cake using 4 eggs. (If mum's 'baking mug' was a standard cup!)

So I've done a trial run using 3 eggs, half a block of butter, half a cup of cocoa, 1/2 a cup of SR flour and 3/4 cup of granulated sugar. The mixture looks right and tastes almost right - could perhaps be a little sweeter.

It's in the oven now.

One of my dc is currently 'cleaning' the mixing bowl. Doesn't look like there will much to wash off It can't taste too bad!

No food colouring in the Red Devil’s Food cake, but it does include some vanilla. The cocoa makes it dark, darker after cooking than in the bowl.
I use an old Betty Crocker recipe.

Did it turn out as wished for?!

Hasn't risen as much as I remember. Possibly needed baking powder. Otherwise, looks good. Have decided not to taste it, but to use it in the birthday cake, so will report back on taste after the birthday.

Verdict: dark and delicious. Lack of sweetness offset beautifully by buttercream. No complaints from the eaters! But IMO a little too dry and a little too dense. Definitely needs more sugar, which would make it less dry I think. Dense, but not heavy, so either I should have baked it in a smaller tin, or it needs some extra raising agent. As cocoa powder makes cake texture tougher, I suspect baking powder would help here.

More experimentation needed!

Hmmm I'm wondering about combining this recipe with the American style cake that uses buttermilk as well....